Four-stranded mini microtubules formed by Prosthecobacter BtubAB show dynamic instability

Abstract

Microtubules, the dynamic, yet stiff hollow tubes built from αβ-tubulin protein heterodimers, are thought to be present only in eukaryotic cells. Here, we report a 3.6-Å helical reconstruction electron cryomicroscopy structure of four-stranded mini microtubules formed by bacterial tubulin-like Prosthecobacter dejongeii BtubAB proteins. Despite their much smaller diameter, mini microtubules share many key structural features with eukaryotic microtubules, such as an M-loop, alternating subunits, and a seam that breaks overall helical symmetry. Using in vitro total internal reflection fluorescence microscopy, we show that bacterial mini microtubules treadmill and display dynamic instability, another hallmark of eukaryotic microtubules. The third protein in the btub gene cluster, BtubC, previously known as “bacterial kinesin light chain,” binds along protofilaments every 8 nm, inhibits BtubAB mini microtubule catastrophe, and increases rescue. Our work reveals that some bacteria contain regulated and dynamic cytomotive microtubule systems that were once thought to be only useful in much larger and sophisticated eukaryotic cells.

Rescuing microtubules from the brink of catastrophe: CLASPs lead the way

“…Interestingly, in spite of the unique dynamic properties of minus-ends, recent studies reported the structures of minus-ends to be quite similar to plus-ends [20,73], indicating that microtubule dynamics are likely defined by a myriad of features at the microtubule end. Although microtubule end complexity can, to some extent, be attributed to the large number of individual protofilaments, it is fascinating that polymers assembled from tubulin-like bacterial proteins, BtubA and BtubB, contain only four protofilaments but display the hallmarks of microtubule dynamic instability [74]. Consolidating the intricate processes occurring on nanometer, sub-second scales with the global transitions on micrometer, minute scales will be essential for a conclusive model of microtubule dynamics.…”

A microtubule bestiary: structural diversity in tubulin polymers

“…Interestingly, defined lateral interactions occur in the polymers of BtubA/BtubB, a tubulin-like heterodimer found in many Prosthecobacter species ( Figure 2 ). BtubA/BtubB polymerizes into 4-protofilament “bacterial microtubules” in vitro ( Deng et al. , 2017 ) and perhaps 5-protofilament polymers in cells ( Pilhofer et al.…”

Computational analysis of filament polymerization dynamics in cytoskeletal networks

“…Microtubules as well as some prokaryotic actin-related proteins, show a behavior termed dynamic instability, where one end of the filament shows phases of growth that are stochastically interrupted by rapid depolymerization events (Deng et al, 2017; Garner, Campbell, & Mullins, 2004; Horio & Hotani, 1986; Mitchison & Kirschner, 1984; Sammak & Borisy, 1988). In contrast, filaments formed by actin and by the bacterial tubulin-homolog FtsZ are known for treadmilling behavior (Fujiwara, Takahashi, Tadakuma, Funatsu, & Ishiwata, 2002; Loose & Mitchison, 2014; Wang, 1985; Wegner, 1976).…”